Since a hearing aid is attached to an ear, a main body is formed small and a microphone for collecting a surrounding sound of the main body and a speaker for outputting a sound amplified by hearing aid processing are placed at near positions. Thus, an acoustic feedback of outputting an annoying sound from the speaker is likely to occur, which is caused by forming an acoustic loop in which a sound output by the speaker goes around the main body and is again collected in the microphone is formed. Particularly, it easily occurs when a hearing aid is not attached to an ear, because a substance for cutting off the sound going around the main body does not exist.
A hearing aid in which the time from turning on power of a main body to attaching the hearing aid to an ear is preset and a speaker starts to output a sound subjected to hearing aid processing after a lapse of the preset time since the power of the main body has been turned on is disclosed (for example, see Patent Document 1).